Fluorescence Lab Julia Schmitz CHEM 250 March 28, 2002
Feb 02, 2016
Fluorescence Lab
Julia SchmitzCHEM 250
March 28, 2002
Frank-Condon Principle
What is Fluorescence?
How a LASER works
Our LASER
• Nitrogen Laser• ¼ - meter monochromator• Digital oscilloscope• Computer-interfaced boxcar
Purpose of this Lab
• Record luminescence spectrum• Record Decay Curve• Investigate Quenching • Determine Lifetime
What is anthracene
• Aromatic hydrocarbon• Easily excited at 337 nm
What is pyrene
• Absorbs strongly at wavelength of Nitrogen Laser
• Fairly long excited-state lifetime
Calculating Energies
References• Anthracene.
http://omlc.ogi.edu/spectra/PhotochemCAD/html/anthracene.html. Internet. Accessed 3/25/02
• Atkins, Peter. Physical Chemistry. W.H. Freeman and Company, New York, 6th ed. 1998.
• Van Dyke, D. A; Pryor, B. A.; Smith, P. G.; Topp, M. R. J. Chem. Educ. 1998, 75, 615-620. Nanosecond Time-Resolved Fluorescence Spectroscopy in the Physical Chemistry Laboratory: Formation of the Pyrene Excimer in Solution.
• Van Dyke, D. A; Pryor, B. A.; Smith, P. G.; Topp, M. R. J. Chem. Educ. 1998, 75, 615-620. Nanosecond Time-Resolved Fluorescence Spectroscopy in the Physical Chemistry Laboratory: Formation of the Pyrene Excimer in Solution. Journal of Chemical Education. Vol 75. No 5. May 1998.
• Piepho, Susan. Laser Lab Handout. Instrumental Setup for LabVIEW-Controlled Fluorescence and Phosphorescence Experiments. March 11, 2002.
Fluorescence Spectra and Decay Lifetimes
K. Nicole CrowderMarch 28, 2002
Intermediate Lab 250
Absorption Spectrum of Anthracene
• This UV/Vis spectrum shows peaks at 324, 340, 356, and 376 nm.
Energies of Absorbance, in cm-1
Peaks Energy for +2 nm
Energy for nm
Energy for –2 nm
324 31056 30864 30675
340 29586 29412 29240
356 28249 28090 27933
376 26738 26596 26455
Fluorescence Spectrum of Anthracene
• The spectrum shows absorbance at 386, 404, 428, and 456 nm.
Energies of Fluorescence, in cm-1
Peaks Energy for +2 nm
Energy for nm
Energy for –2 nm
386 26042 25907 25773
404 24876 24752 24631
428 23474 23364 23256
456 22026 21930 21834
Energy Spacing in Absorption vs. Fluorescence Spectra
Peaks Absorption Fluorescence
1 to 2 1452 1155
2 to 3 1322 1388
3 to 4 1494 1434
Fluorescence Spectrum of 10-5M Pyrene solution
• The fluorescence of pyrene was monitored from at 350 to 500 nm.
Fluorescence Spectrum of 10-3M Pyrene solution
• The same conditions were used for this new concentration, although at 1 nm intervals.
Lifetime of the Excited State of Anthracene and Pyrene
• What is the lifetime, ?• For a first-order decay, I = Io e
kobst
•This can also be expressed as I = 0.37 Io.
•This is quite easy to measure.
Lifetime of Anthracene
Without N2
With N2
Lifetime of 10-5M Pyrene solution
Without N2
With N2
Lifetime of Monomer and Excimer in 10-3M Pyrene solution
Monomer
Excimer
Decay Curves of Pyrene
Courtney ArnottMarch 28, 2002
CHEM 250
Data Collection
• N2 bubbled through sample
• Measured fluorescence emission• Data collected in LabVIEW• What Order??
Points to consider…
• Export data into Excel• Plot curves• Line of best fit• Linear through several lifetimes!!• Wavelength = 387nm (for
monomer)• Quenching
Quenching
• Using molecular O2 to accelerate breakdown of decay curve
• Can stop quenching with other gases
• Result? N2 addition is significant
W/O N2 W/ N2
Monomer vs. Excimer
• Monomer – excited molecule
• Excimer – excited dimer
• Varies with concentration
Figure from Van Dyke et.al, JChemEd Vol 75 No 5 p. 618
Zeroth Order Plot
First Order Plot
Second Order Plot
Conclusions?
• R2 Values– 0th = .9455– 1st = .9939– 2nd = .8821
• Follows 1st order decay curve
• Success!
Further Research
• Study other compounds suggested• Overcoming quenching with other
gases• Examine phosphorescence• Look at monomer and excimer